Megan McCardles on vaccinations:

I’m opposed to many sorts of state interventions, but public health measures strike me as a no-brainer. I mean real public health measures: not nannying people about their trans-fat consumption, but preventing the transmission of infectious disease. The negative externalities of infection seem to me to give the state a perfect right–indeed, an obligation–to curtail your freedom to fanny about spreading cholera.

Vaccines work primarily not by protecting you, but by creating “herd immunity”: denying the virus a reservoir in which to incubate. Public schools* used to be the perfect incubators, because there you have large numbers of people with no prior immunity herded together, making disease transmission a near-certainty. Vaccines have destroyed those disease reservoirs.

Now that the disease reservoirs are destroyed, of course, parents are tempted to free ride on society. They trust in other parents to vaccinate their children, thus maintaining a disease-free environment in which their own precious princes and princesses can run around safely without taking precautions. They do this for reasons logical and illogical–vaccines do pose some very small risk to kids, but more of their fears seem to be based on junk science like the thimerosol-autism connection. But even their real fears about the safety of the vaccine would be vastly outweighed by their fears of disease if other parents didn’t vaccinate, so it’s accurate to describe their behavior as free riding.

I agree with every word, although I still oppose mandating the HPV vaccine.